Eventos Anais de eventos
CONEM 2022
XI Congresso Nacional de Engenharia Mecânica - CONEM 2022
APPROACH FOR THE ABSORPTIVITY ESTIMATION OF A NON-GRAY SURFACE BOUNDING PARTICIPATING MEDIA
Submission Author:
Cesar Augusto Basso , RS , Brazil
Co-Authors:
Cesar Augusto Basso, Guilherme Crivelli Fraga, Roberta Juliana Collet da Fonseca, Francis França
Presenter: Francis França
doi://10.26678/ABCM.CONEM2022.CON22-0670
Abstract
The thermal radiation is a complex phenomenon, and of great importance for processes that involve high temperatures, such as combustion. Therefore, to evaluate these usual engineering problems, such as the design of combustion chambers, furnaces and ovens, it is essential to evaluate the heat transfer by radiation. However, these problems attain an even higher degree of complexity, due to the possible presence of participating media, such as carbon dioxide and water vapor, common combustion products. These chemical species, are called participating media due to their influence on the thermal radiation that permeates them, by absorbing a portion of the incoming radiation, or also by emission. This occurs at different portions of the spectrum, depending on local thermodynamic factors and the species of interest, increasing the complexity to model these systems. In order to solve these problems, it can be employed the line-by-line integration (LBL) of the radiation intensity over the entire spectrum, which is the benchmark solution, providing the exact result, but at a high computational cost. To overcome this computational limitation, several models were developed over the years, such as the gray-gas (GG) model or the weighted-sum-of-gray-gases (WSGG), which are excellent models to represent the thermal radiation transfer across participating media. However, they are limited to be used with black and gray boundaries, while most of engineering problems have the presence of non-gray bounding walls. In recent years, researchers were able to employ the WSGG model in testcases involving non-gray bounding walls, with good accuracy when compared to the LBL solution. But it comes with a certain limitation, where a temperature had to be arbitrated in order to perform the total absorptivity calculation for the non-gray wall, form its respective spectral emissivity profile. The objective of this study is to perform an in-depth analysis of the total absorptivity of a non-gray surface, subjected to incoming radiation from a black surface that has travelled across a participating media with a non-uniform temperature distribution. This media is composed of carbon dioxide and water vapor. Multiple reference temperatures were evaluated, based on the temperature profile studied. From the results obtained, it is possible do estimate a reference temperature that provides accurate results, and a good estimation of the total absorptivity of a non-gray surface.
Keywords
thermal radiation, numerical heat transfer, non-gray walls, participating media
